Apparatus for manufacturing silicon single crystal, method for manufacturing silicon single crystal, and silicon single crystal

ABSTRACT

The apparatus for manufacturing a silicon single crystal includes: a crucible for storing molten silicon; a pulling-up device for pulling up a silicon single crystal from the molten silicon in the crucible to grow; a detecting device for detecting a position of the crucible in a vertical direction; and a control device for controlling a pulling rate for the silicon single crystal by the pulling-up device, based on the detected position of the crucible.

The present application is a divisional of U.S. patent application Ser.No. 11/192,039, filed on Jul. 29, 2005, now U.S. Pat. No. 7,368,011 forwhich priority is claimed under 35 U.S.C. § 121. This application alsoclaims priority under 35 U.S.C. § 119(a) on Patent Application No.2004-226589 filed in Japan on Aug. 3, 2004. The entire contents of eachof these applications are herein fully incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method formanufacturing a silicon single crystal which is manufactured by pullingup a silicon single crystal by the Czochralski method (the CZ method),and to a silicon single crystal which is manufactured by using thisapparatus or method.

2. Background Art

A silicon single crystal is manufactured by heating up a polycrystallinesilicon raw material filled in a crucible using a heater to obtain amolten silicon, and pulling up a silicon single crystal from the moltensilicon to grow by the CZ method. A silicon wafer is manufactured byslicing (cutting) the silicon single crystal which is manufactured bythe above described method, and integrated circuits is formed on thesilicon wafer. Considering a formation of the integrated circuits on thesilicon wafer, it is desirable that the silicon wafer has a high qualityin which the number of COPs (Crystal Originated Particles) exerting aninfluence on a gate oxide integrity of the silicon wafer is small. It iswell known that COPs occur inside OSF (Oxidation Induced Stacking Fault)rings and dislocation clusters and the like occur when a pulling rate isreduced. Furthermore, it is also known that a distribution of thesedefects depends on a value (V/G) which is a ratio of the pulling rate Vof the silicon single crystal and a temperature gradient G in a verticaldirection in a vicinity of a solid-liquid interface of the siliconsingle crystal. That is to say, it is necessary to keep the value of V/Gwithin a predetermined range in order to manufacture a single crystal inwhich the number of COPs is low (largely depends on a distribution ofdefects) with a stabile quality.

However, since the temperature gradient G changes due to various factorsin a mass production of the silicon single crystals, in the case inwhich the silicon single crystal is pulled up at a constant pulling rateV, the value of V/G varies, and as a result, the product quality of thesilicon single crystals varies widely. In the following Patent documents1 and 2, methods for manufacturing silicon single crystals having nodefects in which a temperature gradient of the silicon single crystal ina lengthwise direction (a vertical direction) is measured using a noncontact temperature sensor, and a pulling rate for the silicon singlecrystal is controlled based on the measured temperature gradient so asto keep the value of V/G within a predetermined range.

However in the above described prior art, the measurement valuesmeasured by the temperature sensor varies greatly, depending on aposition of the temperature sensor with respect to the silicon singlecrystal which is pulled out. Accordingly, it is necessary to adjust theposition of the temperature sensor precisely for each production batch,and a lot of work and time are required for arranging and managing thetemperature sensor. Here, the production batch means a whole set ofprocesses performed to manufacture one silicon single crystal. Since alarge number of apparatuses for manufacturing silicon single crystalsare provided in a factory for silicon single crystals, in the case inwhich temperature sensors are employed for each of them, there is aproblem in which a lot of work is required. Also, there is a problem inwhich a cost of the apparatus for manufacturing the silicon singlecrystal is increased by the provision of the temperature sensor.Furthermore, there is also a problem that, in the case in which thetemperature sensor is provided in the apparatus for manufacturingsilicon single crystals, a working efficiency of doing maintenance in aninterior of the apparatus (for example, changing carbon members in afurnace and the like) is deteriorated. Due to the above considerations,it would be desirable to keep the value of V/G within the predeterminedrange by some method other than the method of controlling the pullingrate based on the measurement values measured by the temperature sensor.

Patent document 1 Japanese Unexamined Patent Application, FirstPublication No. 2000-143388.

Patent document 2 Japanese Unexamined Patent Application, FirstPublication No. 2001-220285.

SUMMARY OF THE INVENTION

The biggest factors to determine the temperature gradient G when pullingup the silicon single crystal are a structure of a heat insulatingmaterial, and a distance (hereinafter referred to as a gap) between aliquid surface of the molten silicon and a lower end of a heat shieldmember provided over the crucible. Usually, in order to keep this gapconstant for eliminating variations in the product quality between eachsilicon single crystal, the position of the liquid surface of the moltensilicon is adjusted. However, the position of the crucible in thevertical direction varies inevitably between production batches inconsequence of variations in a thickness of the used crucible (i.e. aquartz crucible), deformation of the crucible occurred when melting thepolycrystalline silicon as a raw material, and variations of a shape orindividual differences of a graphite susceptor (the carbon crucible)which holds the crucible. Even in the case in which a minute positionaldeviation of the crucible in the vertical direction is present, a heatconduction of a heat given out from a heating device changes, and as aresult, variations in the temperature gradient G are engendered.

Therefore, it is thought that a silicon single crystal can bemanufactured with a stable product quality by compensating changes ofthe temperature gradient G which are generated by changes of theposition of the crucible in the vertical direction.

The present invention has been accomplished in the light of the aboveproblems, and one object is to provide an apparatus and a method formanufacturing a silicon single crystal in which the pulling rate isadjusted based on the position of the crucible in the verticaldirection. The other object is to provide a silicon single crystalmanufactured using the apparatus or the method for manufacturing asilicon single crystal.

In order to solve the above described problems, an apparatus formanufacturing a silicon single crystal of the present inventionincludes: a crucible for storing molten silicon; a pulling-up device forpulling up a silicon single crystal from the molten silicon in thecrucible to grow; a detecting device for detecting a position of thecrucible in a vertical direction; and a control device for controlling apulling rate for the silicon single crystal by the pulling-up device,based on the detected position of the crucible.

In the apparatus for manufacturing a silicon single crystal of thepresent invention, the control device may calculate an average crucibleposition by taking an average of positions of the crucible in thevertical direction during manufacturing silicon single crystals over aplurality of times in the past, and the control device may control thepulling rate for the silicon single crystal based on an amount ofpositional deviation which is a value obtained by subtracting theaverage crucible position from the detected position of the crucible.

The control device may set the pulling rate for the silicon singlecrystal to be higher than an initial speed which is set in advance whenthe amount of positional deviation is positive, and the control devicemay set the pulling rate for the silicon single crystal to be lower thanthe initial speed when the amount of positional deviation is negative.

The control device may set the pulling rate for the silicon singlecrystal higher or lower within a range from 0% to 5% of the initialspeed per 1 mm of the amount of positional deviation.

The control device may calculate a standard deviation σ of the positionsof the crucible in the vertical direction during manufacturing thesilicon single crystals over a plurality of times in the past, and thecontrol device may control the pulling rate for the silicon singlecrystal as the amount of positional deviation being 3σ when the amountof positional deviation is larger than 3σ.

In order to solve the above described problems, a method formanufacturing a silicon single crystal of the present inventionincludes: a detecting step of detecting a position in a verticaldirection of a crucible when pulling up a silicon single crystal from amolten silicon in the crucible to grow; and a control step ofcontrolling a pulling rate of the silicon single crystal, based on thedetected position of the crucible.

In the method for manufacturing a silicon single crystal of the presentinvention, the control step may further includes: a step of calculatingan average crucible position by taking an average of positions of thecrucible in the vertical direction during manufacturing silicon singlecrystals over a plurality of times in the past; and a step ofcontrolling the pulling rate for the silicon single crystal, based on anamount of positional deviation which is a value obtained by subtractingthe average crucible position from the detected position of thecrucible.

In the control step, the pulling rate for the silicon single crystal maybe set to be higher than an initial speed which is set in advance whenthe amount of positional deviation is positive, and the pulling rate forthe silicon single crystal may be set to be lower than the initial speedwhen the amount of positional deviation is negative.

In the control step, the pulling rate for the silicon single crystal maybe set higher or lower within a range from 0% to 5% of the initial speedper 1 mm of the amount of positional deviation.

The control step may further includes: a step of calculating a standarddeviation σ of the positions of the crucible in the vertical directionduring manufacturing the silicon single crystals over a plurality oftimes in the past, and a step of controlling the pulling rate for thesilicon single crystal as the amount of positional deviation being 3σwhen the amount of positional deviation is larger than 3σ.

A silicon single crystal of the present invention is manufactured usingany one of apparatuses and methods for manufacturing a silicon singlecrystal described above.

In the apparatus and the method for manufacturing a silicon singlecrystal silicon single crystal, the pulling rate for the silicon singlecrystal is controlled based on the detected position of the crucible inthe vertical direction. As a result, even in the case in which a heatconduction of a heat given out from a heating device varies depending onthe position of the crucible in the vertical direction, the pulling ratefor the silicon single crystal is controlled so as to compensate for thevariations of the heat conduction. Therefore, it is possible to keep avalue (V/G) of a ratio of the pulling rate V of the silicon singlecrystal and a temperature gradient G in a vertical direction in avicinity of a solid-liquid interface of the silicon single crystalwithin a predetermined range, which is extremely important from thepoint of view of determining defect generation regions such as densityand distribution of COPs (defects) and the like. As a result, it ispossible to manufacture a silicon single crystal with a stable productquality.

Here, in order to suppress variations of the product quality of thesilicon single crystal, it is desirable to adjust the pulling rateminutely based on a feedback of a relative change of the position of thecrucible in the vertical direction. In order to do this, an averagecrucible position may be calculated by taking an average of positions ofthe crucible in the vertical direction during manufacturing siliconsingle crystals over a plurality of times in the past, and the pullingrate for the silicon single crystal may be controlled based on an amountof positional deviation which is a value obtained by subtracting theaverage crucible position from the detected position of the crucible.

In this case, the pulling rate for the silicon single crystal isminutely adjusted based on the relative change of the position of thecrucible in the vertical direction, and as a result, it is possible tosuppress the variations of the product quality of the silicon singlecrystal.

In the case in which the amount of positional deviation is positive, thepulling rate for the silicon single crystal may be set to be higher thanan initial speed which is set in advance. In the case in which theamount of positional deviation is negative, the pulling rate for thesilicon single crystal may be set to be lower than the initial speed.

In the case in which the amount of the positional deviation is positiveand thus the position of the crucible in the vertical direction is high,a proportion of the heat conduction from a bottom portion of thecrucible is high, and the temperature gradient G becomes large.Considering these, the pulling rate for the silicon single crystal isset to be higher than the initial speed which is set in advance.Conversely, in the case in which the amount of the positional deviationis negative and thus the position of the crucible in the verticaldirection is low, the proportion of the heat conduction from a sideportion of the crucible is high, and the temperature gradient G becomessmall. Considering these, the pulling rate for the silicon singlecrystal is set to be lower than the initial speed which is set inadvance. By doing these, since it is possible to keep the value of V/Gwithin the predetermined range even in the case in which the position ofthe crucible in the vertical direction varies, it is possible tomanufacture a silicon single crystal with a stable product quality.

The pulling rate for the silicon single crystal may be set to be higheror lower within a range from 0% to 5% of the initial speed per 1 mm ofthe amount of positional deviation. That is, the pulling rate may becontrolled to be limited to the above range. Thereby, it is possible toprevent the occurrence of a state in which a compensation amount for thepulling rate for the silicon single crystal becomes too large and thevariations in the product quality of the silicon single crystal occur.

Furthermore, a standard deviation σ of the positions of the crucible inthe vertical direction during manufacturing the silicon single crystalsover a plurality of times in, the past may be calculated, and in thecase in which the amount of positional deviation is larger than 3σ, thepulling rate for the silicon single crystal may be calculated as theamount of positional deviation being 3σ. Thereby, it is possible toprevent the occurrence of a state in which a compensation amount for thepulling rate for the silicon single crystal becomes too large and thevariations in the product quality of the silicon single crystal occur.

According to the present invention, since the pulling rate for thesilicon single crystal is controlled based on the detected position ofthe crucible in the vertical direction, it is possible to manufacture asilicon single crystal with stable product quality.

Under conditions by which OSF regions are formed, in the resultsobtained using the above described apparatus and the method formanufacturing a silicon single crystal according to the presentinvention, the variation in the distribution of the OSF diameter isless, as compared with the results without using the apparatus and themethod. Accordingly, silicon single crystals can be manufactured ofwhich product quality is stabilized. For example, silicon singlecrystals can be manufactured of which diameters are 200 mm and externaldiameters of OSF rings are in a range from 13.2 cm to 14.4 cm. Underconditions by which OSF rings are closed and no dislocation clusters aregenerated, in the results obtained using the above described apparatusand the method for manufacturing a silicon single crystal according tothe present invention, dislocation cluster faults are reduced.Accordingly, silicon single crystals can be manufactured of whichproduct quality is stabilized. For example, silicon single crystals canbe manufactured in which dislocation cluster faults are reduced by 5%,as compared with the results without using the apparatus and the method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a figure showing an overall structure of an embodiment of theapparatus for manufacturing a silicon single crystal according to thepresent invention.

FIG. 2 is a figure showing an example of a relationship between theamount of the positional deviation of the crucible from the averagecrucible position, and compensation amount for the pulling rate.

FIG. 3 is a figure showing the position of the crucible, thecompensation amount for the pulling rate, and the average crucibleposition during manufacturing a silicon single crystal according to anexample of the present invention.

FIG. 4 is a figure showing an example of measurement results forexternal diameters of OSF rings in silicon wafers manufactured using theapparatus and the method for manufacturing a silicon single crystal ofthe present invention, and those manufactured without using the same.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the apparatus and the method for manufacturinga silicon single crystal according to the present invention will beexplained in detail with reference to the figures. FIG. 1 is a figureshowing an overall structure of an apparatus for manufacturing a siliconsingle crystal according to the preferred embodiment of the presentinvention. As shown in this figure, this apparatus of the preferredembodiment includes a main body portion 10, a pulling-up device 11, anda control device 12. In a chamber 21 of the main body portion 10, thereis provided a crucible 22 which receives molten silicon M, and an outercircumferential surface of this crucible 22 is covered over by agraphite susceptor 23. The crucible 2 is made from quartz or the like.

Via the above described graphite susceptor 23, a bottom surface of thecrucible 22 is fixed to an upper end of a support shaft 24, and a lowerportion of this support shaft 24 is connected to a crucible drive devicewhich is not shown in the figure. This crucible drive device not shownin the figures includes a first motor for rotation which rotates thecrucible 22 in a horizontal position, and a motor for lifting andlowering the crucible 22. By the actions of these two motors, thecrucible 22 can rotate in the horizontal position, while it can beshifted in a upwards and a downwards directions. In a neighborhood ofthe crucible 22, there is provided a detecting device 25 which detects aposition of the crucible 22 in a vertical direction.

Although, in FIG. 1, the detecting device 25 is shown in a simplifiedmanner, this detecting device 25 may be a device such as a potentiometeror the like which detects the position of the crucible 22 in thevertical direction in a non contact manner, for example, by irradiatinga laser light, ultrasonic waves or the like to an upper end of an outercircumferential portion of the crucible 22. Results of this detection bythe detecting device 25 is outputted to the control device 12. The outercircumferential surface of the crucible 22 is surrounded by a heater 26which is arranged with a predetermined gap spacing between them. Anouter circumferential surface of this heater 26 is surrounded by aninsulation tube 27 which is arranged with a predetermined gap spacingbetween them. The heater 26 includes, for example, a high frequencyheating device or a resistance heating device, and heats and melts apolycrystalline silicon of high purity charged into the crucible 22 intothe molten silicon M.

Detection of the position of the crucible 22 in the vertical directionby the detecting device 25 is performed by taking a lower edge of a coneportion 30 b, or an upper edge of the heater 26 as a standard, or bytaking a combination of these as a standard, and detecting a relativevertical position of an upper edge of the crucible 22 with respect tothis standard. Here, each of the position in the vertical direction ofthe lower edge of the cone portion 30 b and the position in the verticaldirection of the upper edge of the heater 26 taken as a standard may bedifferent for each example of this apparatus, or may be different foreach production batch. Therefore, for each production batch, whensetting up for pulling up the silicon single crystal, the position takenas the standard is confirmed by the detecting device 25. Furthermore,there is also a possibility that the position of the crucible 22 on thesupport shaft 24 may be different for each example of this apparatus, ormay be different for each production batch. Therefore, for eachproduction batch, when setting up for pulling up the silicon singlecrystal, the position of the crucible 22 is confirmed by the detectingdevice 25 for this reason as well.

A casing 28 shaped as a circular cylinder is connected at an upper endof the chamber 21. A pulling-up device 11 is provided at an upper endportion of this casing 28. The pulling-up device 11 includes a pullingup head (not shown in the figure) which is provided so as to be able torotate in a horizontal position, a second motor for rotation (also notshown in the figure) which rotates the pulling up head in the horizontalposition, a pulling up wire W which extends vertically downwards fromthe pulling up head towards a rotational center of the crucible 22, anda pulling up motor (likewise not shown in the figure) which is providedin the pulling up head and winds up or pays out the pulling up wire W.At a lower end of the pulling up wire W, there is attached a seedcrystal 29 for being dipped into the molten silicon M and pulling up asilicon single crystal SI.

Between an outer circumferential surface of the silicon single crystalSI and an inner circumferential surface of the crucible 22, there isprovided a heat shield member 30 which surrounds the outercircumferential surface of the silicon single crystal SI. This heatshield member 30 is formed in a generally circular tubular shape, and itincludes a tubular portion 30 a which intercepts radiant heat from theheater 26, the cone portion 30 b which extends in a downwards andinwards direction from a lower edge of the tubular portion 30 a so thatits diameter becomes progressively smaller, and a flange portion 30 cwhich extends outwards from an upper edge of the tubular portion 30 a inapproximately the horizontal direction. By the outer edge of the abovedescribed flange portion 30 c being mounted to the upper edge of theinsulation tube 27, this heat shield member 30 is fixed within thechamber 21 so that the lower edge of the cone portion 30 b is positionedat just a predetermined distance above the surface of the molten siliconM. This heat shield member 30 is made from graphite.

The control device 12 controls the pulling rate for the silicon singlecrystal SI based on the position in the vertical direction of thecrucible 22 detected by the detecting device 25. In concrete terms, thecontrol device 12 stores positions of the crucible 22 in the verticaldirection during the manufacturing procedure for a silicon singlecrystal SI over a plurality of times in the past (i.e. for a number ofpast production batches), and calculates an average crucible position bytaking an average of them. And it controls the pulling rate for thesilicon single crystal SI based on an amount of positional deviationwhich is a value obtained by subtracting the average crucible positionfrom the detected position of the crucible obtained by the detectingdevice 25.

Here, it is desirable for the number of production batches n forobtaining the above described average crucible position to be made to apredetermined number or more, since in the case in which it is toosmall, an accuracy is deteriorated. And it is also desirable for thisnumber to be kept the other number or less. Because since in the case inwhich the number of production batches n is too large, cruciblepositions which vary greatly for example before and after changing thecrucible 22 and the susceptor 23 are included, resulting indeterioration of the accuracy as well. It is preferable to set thenumber of the production batches n within a range from 3 to 25, and itis more preferable to set n to about 7 or 8. Here it is understood thatthe number of production batches performed in a single month with suchan apparatus for manufacturing a silicon single crystal is about 10 to20.

It is desirable to compensate the pulling rate for the silicon singlecrystal SI which is controlled by the control device 12 within a rangefrom 0% to 5% of an initial speed which is determined in advance, per 1mm of the amount of the positional which is a value obtained bysubtracting the average crucible position from the detected position ofthe crucible. Here, the control device 12 sets the pulling rate for thesilicon single crystal to be higher than the above described initialspeed, in the case in which the above described amount of the positionaldeviation is positive (in other words, in the case in which the crucible22 is positioned at or above the average crucible position). In the casein which the amount of the positional deviation is negative (in otherwords, in the case in which the crucible 22 is positioned below theaverage crucible position), the control device 12 sets the pulling ratefor the silicon single crystal to be lower than the above describedinitial speed.

In the case in which the compensation amount for the pulling rate forthe silicon single crystal SI is set to be larger than 5% of the initialspeed, this compensation amount is too large. Therefore, according tothis preferred embodiment of the present invention, the compensationamount for the pulling rate is limited to within 5% of the initialspeed. Furthermore, in the case in which the crucible 22 is positionedabove the average crucible position (i.e., in the case in which theabove described amount of positional deviation is positive), theproportion of heat conduction from the bottom portion of the crucible 22is increased, and the temperature gradient G becomes large. Consideringthese, the value of V/G is constrained to be within a predeterminedrange by setting the pulling rate for the silicon single crystal to behigher than the above described initial speed. Conversely, in the casein which the crucible 22 is positioned below the average crucibleposition (i.e., in the case in which the above described amount ofpositional deviation is negative), the proportion of heat conductionfrom the side portion of the crucible 22 is increased, and thetemperature gradient G becomes small. Considering these, the value ofV/G is constrained to be within the predetermined range by setting thepulling rate for the silicon single crystal to be lower than the abovedescribed initial speed.

Furthermore, in the preferred embodiment of the present invention, thecontrol device 12 calculates a standard deviation σ of the positions ofthe crucible 22 in the vertical direction during the manufacturingprocedure for the silicon single crystal SI over a plurality of times inthe past (i.e. for a number of past batches). And, in the case in whichthe above described amount of the positional deviation is outside arange of −3σ to +3σ, this amount of the positional deviation is set to−3σ or +3σ respectively. This is to limit the compensation amount forthe pulling rate for the silicon single crystal SI in the same manner asdescribed above.

FIG. 2 is a figure showing an example of a relationship between theamount of the positional deviation of the crucible 22 from the averagecrucible position, and the compensation amount for the pulling rate. Asshown in FIG. 2, in the case in which the amount of the positionaldeviation from the average crucible position of the crucible 22 iswithin the range of −3σ to +3σ and the amount is positive, thecompensation amount for the pulling rate increases almost proportionallyto the amount of the positional deviation. Conversely, in the case inwhich the amount of the positional deviation is negative, thecompensation amount for the pulling rate decreases almost proportionallyto the amount of positional deviation.

In the case in which the amount of the positional deviation of thecrucible 22 from the average crucible position exceeds +3σ, thecompensation amount for the pulling rate is set to the same value asthat when the amount of positional deviation is +3σ. Conversely, in thecase in which the amount of the positional deviation of the crucible 22from the average crucible position is lower than −3σ, the compensationamount for the pulling rate is set to the same value as that when theamount of positional deviation is −3σ.

In order to manufacture the silicon single crystal SI using theapparatus of the above described structure, first, the polycrystallinesilicon raw material charged in the crucible 22 is heated up with theheater 26 and is melted to molten silicon M, and a temperature of thismolten silicon M is heated to and kept a predetermined temperature.Next, the position of the crucible 22 in the vertical direction is setso that a gap between a liquid surface of the molten silicon M filled inthe crucible 22 and a lower end of the heat shield member 30 (the loweredge of its cone portion 30 b) provided at the upper portion of thecrucible 22 becomes equal to a predetermined distance. Next, a seedcrystal 29 is fixed to a lower tip of the pulling up wire W, and thepulling up wire W is lowered downwards so that a lower end of the seedcrystal 29 comes into contact with a surface of the molten silicon M.The pulling up upwards of the silicon single crystal SI is started fromthis state.

When pulling the pulling up wire W upwards, along with rotating thecrucible 22 at a rotational speed of for example about 0.1 to 20 min⁻¹,the silicon single crystal SI which is being pulled out is rotated inthe opposite direction at a rotational speed of for example about 1 to25 min⁻¹. Here, it should be understood that when pulling up the siliconsingle crystal SI, it may also be the case that the crucible 22 and thesilicon single crystal SI are both rotated in the same direction.

The results from the detecting device 25 of its detection of theposition of the crucible 22 in the vertical direction are outputted tothe control device 12 during the process of pulling up the siliconsingle crystal SI. The control device 12 calculates the amount of thepositional deviation of the crucible 22 by subtracting this detectedresult from the average crucible position. Here, it should be understoodthat the explanation has followed a course in which the average crucibleposition is calculated by the control device 12 after the manufacturingprocedure for the silicon single crystal SI has been performed aplurality of times in the past, so that a track record has beenestablished. On the other hand, when initially manufacturing the firstsilicon single crystal SI after having set up this apparatus formanufacturing a silicon single crystal, this average crucible positionhas not yet been obtained. Therefore, it is desirable, at this time, forexample, to follow the procedure of taking the position of the cruciblein the vertical direction at the time of starting the manufacture of thesilicon single crystal SI as being the average crucible position on atemporary basis.

After the amount of positional deviation of the crucible 22 iscalculated, the control device 12 calculates compensation amount for thepulling rate for the silicon single crystal SI by using the amount ofthe positional deviation which has been calculated, and the relationshipbetween the amount of positional deviation of the crucible 22 from theaverage crucible position and the compensation amount for the pullingrate shown in FIG. 2. Using this compensation amount for the pullingrate, the pulling rate is obtained by compensating the initial speedwhich has been set in advance. And a control signal which corresponds tothis pulling rate is outputted to the pulling-up device 11, and therebythe pulling rate for the silicon single crystal SI is controlled.

In the case in which the crucible 22 is positioned so as to be higherthan the average crucible position, due to this speed compensation, thepulling rate of the silicon single crystal is set to be higher than theabove described initial pulling rate. On the other hand, in the case inwhich the crucible 22 is positioned so as to be lower than the averagecrucible position, the pulling rate of the silicon single crystal is setto be lower than the above described initial pulling rate. By doingthis, it is possible to keep the value of V/G within the predeterminedrange, and it is possible to manufacture a silicon single crystal withstable product quality. It should be understood that, when manufacturingthe silicon single crystal SI in this manner, the control device 12 alsoperforms control by minutely adjusting the position of the liquidsurface of the molten silicon M so as to keep constant the distance (thegap) between the liquid surface of the molten silicon M charged in thecrucible 22, and the lower end of the heat shield member 30 (the loweredge of its cone portion 30 b) provided at the upper portion of thecrucible 22.

EXAMPLES

The inventors have manufactured silicon single crystals SI using theabove described apparatus and method for manufacturing a silicon singlecrystal. In the examples, silicon single crystals SI of diameter 200 mmwere manufactured. FIG. 3 is a figure showing the crucible position, thecompensation amount for the pulling rate, and the like duringmanufacturing a silicon single crystal according to the preferredembodiment of the present invention. Here, in FIG. 3, the batch numberis shown along the horizontal axis, while the compensation amount forthe pulling rate, and the average crucible position and the actualposition of the crucible are shown along the vertical axis.

Referring to FIG. 3, it is understood that the position of the crucible22 in the vertical direction (the actual position of the crucible) doesnot change excessively from batch to batch, but it is not constant andchanges little by little between batches. Also, when the averagecrucible position (the crucible position averaged over the last sevenbatches) is considered, with increase of the batch number, this positionchanges gradually in a constant direction (in the example shown in FIG.3, the upwards direction).

Moreover, when the compensation amount for the pulling rate and theposition of the crucible 22 in the vertical direction (the actualposition of the crucible) are compared together, it is understood thatthere is also a tendency for the compensation amount for the pullingrate to change according to a change of the position of the crucible 22in the vertical direction. In other words, in the case in which theposition of the crucible 22 in the vertical direction is low (forexample, when the batch number is 2), the compensation amount for thepulling rate assumes a negative value. In contrast, in the case in whichthe position of the crucible 22 in the vertical direction is high (forexample, when the batch number is 3), the compensation amount for thepulling rate assumes a positive value.

FIG. 4 is a figure showing an example of measurement results forexternal diameters of OSF rings in silicon wafers manufactured using theapparatus and the method for manufacturing a silicon single crystal ofthe present invention, and those manufactured without using the same. Inthis figure, the batch number is shown along the horizontal axis, andthe external diameter of the OSF ring (its average total length) isshown along the vertical axis. Here, in FIG. 4, results of which thebatch number is twelve or less are obtained without using the apparatusand the method for manufacturing a silicon single crystal according tothe present invention. Results of which the batch number is thirteen orlarger are obtained using the apparatus and the method for manufacturinga silicon single crystal according to the present invention.

As shown in FIG. 4, under conditions by which OSF regions are formed, inthe results obtained using the above described apparatus and the methodfor manufacturing a silicon single crystal according to the presentinvention, the variation in the distribution of the OSF diameter isless, as compared with the results without using the apparatus and themethod. Accordingly, it is possible to stabilize the product quality.

Furthermore, under conditions by which OSF rings are closed and nodislocation clusters are generated, in the results obtained using theabove described apparatus and the method for manufacturing a siliconsingle crystal according to the present invention, dislocation clusterfaults are reduced by 5%, as compared with the results without using theapparatus and the method.

Although the present invention has been described above in terms ofpreferred embodiments thereof, it should not be considered as beinglimited to the above described contents; it may be freely varied, withinits legitimate and proper scope. For example, the application of theabove described preferred embodiments to the case of manufacturing asilicon single crystal SI without applying any magnetic field to themolten silicon in the crucible 22 is disclosed by way of example, and isnot limitative of the present invention; it would also be acceptable tomanufacture the silicon single crystal SI while applying a horizontalmagnetic field or a cusp magnetic field to the molten silicon.Furthermore, the present invention is not particularly limited as to thediameter or the size of the silicon single crystal which is manufacturedthereby; it would be possible to apply the present invention to themanufacture of a silicon single crystal having any desired diameter.

Thus, while preferred embodiments of the invention have been describedand illustrated above, it should be understood that these are exemplaryof the invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

1. An apparatus for manufacturing a silicon single crystal, comprising: a crucible for storing molten silicon; a pulling-up device for pulling up a silicon single crystal from the molten silicon in the crucible to grow; a detecting device for detecting a position of the crucible in a vertical direction; and a control device for controlling a pulling rate for the silicon single crystal by the pulling-up device, based on the detected position of the crucible.
 2. An apparatus for manufacturing a silicon single crystal according to claim 1, wherein the control device calculates an average crucible position by taking an average of positions of the crucible in the vertical direction during manufacturing silicon single crystals over a plurality of times in the past, and the control device controls the pulling rate for the silicon single crystal based on an amount of positional deviation which is a value obtained by subtracting the average crucible position from the detected position of the crucible.
 3. An apparatus for manufacturing a silicon single crystal according to claim 2, wherein the control device sets the pulling rate for the silicon single crystal to be higher than an initial speed which is set in advance when the amount of positional deviation is positive, and the control device sets the pulling rate for the silicon single crystal to be lower than the initial speed when the amount of positional deviation is negative.
 4. An apparatus for manufacturing a silicon single crystal according to claim 3, wherein the control device sets the pulling rate for the silicon single crystal higher or lower within a range from 0% to 5% of the initial speed per 1 mm of the amount of positional deviation.
 5. An apparatus for manufacturing a silicon single crystal according to claim 2, wherein the control device calculates a standard deviation σ of the positions of the crucible in the vertical direction during manufacturing the silicon single crystals over a plurality of times in the past, and the control device controls the pulling rate for the silicon single crystal as the amount of positional deviation being 3σ when the amount of positional deviation is larger than 3σ. 